Various methods have been used in the past for permanently joining plastic parts in fluid-tight sealing relation, including heat sealing and solvent-bonding techniques. Heat sealing, although widely used, ordinarily requires elaborate supports and operating mechanisms to achieve reliability and production volume in the assembly of relatively small plastic parts such as, for example, filter housing, couplings, port assemblies, and other elements and assemblies commonly used in medical equipment.
Solvent sealing, which ordinarily involves coating one of the parts with solvent before the two parts are fitted together, is suitable for some operations but has severe limitations for volume production. Parts once coated must be immediately assembled; it is not feasible, for example, to coat successively a multiplicity of parts and then assemble them in a batch-type operation. Also, in those cases where one of the parts contains (or communicates with) a liquid, the usual solvent coating and fitting operations are not only awkward and unwieldly, but present risks of liquid interfering with proper solvent bonding and, even more important, of small amounts of solvent invading the liquid-containing compartment. It is apparent that any contact between the liquid or solvent is undesirable and, especially if it might result in contamination of the liquid (such as parenteral fluid), must be strictly avoided.